The present invention relates to the art of earth boring and more particularly to an improved rotary rock bit. The present invention is especially adapted for use in that type of rotary rock bit popularly known as a three-cone bit; however, its use is not restricted thereto, and the present invention can be used in other types of rotary rock bits.
A three-cone rotary rock bit is adapted to be connected as the lowest member of a rotary drill string. As the drill string is rotated, the bit disintegrates the earth formations to form an earth borehole. The three-cone rotary rock bit includes three individual arms that extend angularly downward from the main body of the bit. The lower end of each arm is shaped to form a spindle or bearing pin. A cone cutter is mounted upon each bearing pin and adapted to rotate thereon. Individual bearing systems promote rotation of the cone cutter. These bearing systems have traditionally been roller bearings, ball bearings, friction bearings, or a combination of the aforementioned bearings. The cone cutters include cutting structure on their outer surfaces that serve to disintegrate the formations as the bit is rotated.
The rotary rock bit must operate under very severe conditions, and the size and geometry of the bit is restricted by the operating characteristics. At the same time, the economics of petroleum production demand a longer lifetime and improved performance from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cones, thereby providing a longer useful lifetime for the cones. This has resulted in the bearing systems being the first to fail during the drilling operation. Consequently, a need exists for improved bearing systems to extend the useful lifetime of the bit.
In addition to rotational forces experienced by the bit, the bit is subjected to a thrust load during operation. The weight of the drill string and in some instances the downward force applied by the rotary drilling equipment apply a substantial thrust load to the bit. The thrust load in combination with the rotational forces tend to force the rollers into a postition askew to the longitudinal axis of the bearing pin. Wear of the roller bearing races tends to exaggerate the skewing problem.
The present invention assists in achieving a more uniform load distribution in the bearing during the drilling operation and lowers contact stress due to reduced misalignment between the rollers and the bearing races. The rollers are guided in such a way as to insure that the axes of the rollers remain parallel to the axis of the bearing pin and aligned with the bearing races to prevent skewing of the rollers during the drilling operation. The present invention also prevents the rollers from sliding against each other. The rollers are spaced symmetrically around the periphery of the bearing pin to help achieve a more uniform load distribution. Heat is dissipated from the bearing surfaces and the lubricant to assist in reducing the operating temperature of the bearing. A split bearing cage with cantilevered spearator elements projecting between the rollers provides a more compatible material for the rollers to slide against. The present invention allows the above advantages to be obtained without requiring a substantially greater amount of space than is normally allocated to the roller bearing system. Space is an extremely important limitation in rotary rock bits, and the ability to increase bearing performance without increasing the space required for the bearing is a substantial improvement.